UV-reflective interference layer system

ABSTRACT

There is provided a UV-reflective interference layer system for transparent substrates with broadband anti-reflection properties in the visible wavelength range. The interference layer system includes at least four individual layers. Successive layers have different refractive indices and the individual layers contain UV and temperature-stable inorganic materials.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation-in-part of (a) U.S.patent application Ser. No. 09/514,437, which was filed on Feb. 28,2000, and (b) International Patent Application PCT/EP00/12878, which wasfiled Dec. 15, 2000. The present application is also claiming priorityof German Patent Application DE 199 62 144.6, filed Dec. 22, 1999.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention concerns a UV-reflective interference layer systemfor transparent substrates with broadband antireflection in the visiblewavelength range, a method for coating a substrate with such a layersystem, and the use of such coating systems in various fields ofapplication.

[0004] 2. Description of the Prior Art

[0005] Currently known glass antireflections for the visible spectralrange, such as the MIROGARD or the AMIRAN antireflection of Schott-DESAGAG, Grünenplan, are interference filters of three layers, wherein alayer with an intermediate index of refraction is first deposited,followed by a layer with high index of refraction, usually TiO₂, andthen a layer with low index of refraction, usually SiO₂ or MgF₂. As thelayer with intermediate index of refraction, for example, a mixture ofSiO₂ and TiO₂, but also Al₂O₃ is used. Such three-layer antireflectionsare deposited, for example, on eyeglass lenses, on monitors, on plateglass, such as display window panels, on treated lenses, etc.

[0006] In most instances, these filters have a blue-violet or greenresidual reflection. When light impinges perpendicularly, the reflectioncharacteristic of glasses coated on both sides is characterized in thatthe reflection within the wavelength interval of around 400-700 nm isless than 1%, for example, but outside this range the reflection risesto values of up to around 30% (V or W-shaped characteristic), i.e., farabove the 8% of uncoated glass.

[0007] The drawback to such systems is that, when viewing at an anglethat increasingly deviates from the perpendicular, the characteristicshifts to ever shorter wavelengths, so that the long-wave reflectionmaximum ends up in the visible range, and produces an undesirable redcomponent to the reflected light color.

[0008] One goal of the present invention is therefore to find anantireflection whose residual reflection is low in a much broaderwavelength range, i.e., in the range from 400 to at least 800 nm withperpendicular incidence of light, and which furthermore also providesbroadband antireflection at rather large viewing angles. In manyapplications, such as display window glazings or glazings for pictures,a neutral-color appearance is in fact desirable, especially fordifferent viewing angles.

[0009] Especially for picture glazings, say, in museums, but also in thecase of display window glazings, furthermore, it is desirable that anantireflecting glass—if possible, color-neutral—at the same timeprovides the function of protecting the colors of the picture or thenatural or synthetic fibers, as well as the dyestuffs of the windowdisplays, against ultraviolet light.

[0010] As is known, the UV component of sunlight or that of lamp light,especially in the case of metal halide or other gas discharge lamps, butalso even with halogen bulbs, is sufficient to cause considerable damageover a lengthy period of time, such as discoloration or embrittlement ofnatural or synthetic fabrics. A UV protection would also be desirablefor glazings in office or residential buildings, in order to greatlyreduce the fading of wood surfaces, draperies, upholstered furniture,etc., under direct sunlight, and thus enable, for example, an improvedpassive utilization of solar energy. Present-day thermal protectionglasses, which contain a thin silver layer, are not antireflective inthe visible range, and furthermore also do not offer sufficient UVprotection, since thin silver layers become transparent in the UV.

[0011] In the case of known antireflective soft glass, UV protection isachieved by the use of organic polymers as absorbers of UV light, forexample, as compound glass, wherein two glass panes are laminatedtogether with a PVB plastic foil adapted by its index of refraction tothe glass, for example, 380 μm in thickness (the glass MIROGARD-PROTECTfrom Schott-DESAG). Such glasses are [used] under intense lamp light,for example, as front panels for lamps, but they are nottemperature-stable and they are also degraded by intensive UV radiation.Also, their three-layer antireflection on one side has theabove-mentioned limitations, and furthermore the production of compoundglass is costly.

[0012] Another possibility is the use of UV-absorbing varnish layers,which are several micrometers thick and are transparent to visiblelight. Such varnish layers are likewise not stable to UV andtemperature, and after being deposited on the glass they must further bemade antireflective. Regarding the state of the art, refer also to thefollowing publications:

[0013] D1: H. Schröder, “Oxide Layers Deposited from Organic Solutions”,in Physics of Thin Films, Academic Press, New York, London, Vol. 5(1969), pp. 87-140

[0014] D2: H. Schröder, Optica Acta 9, 249 (1962)

[0015] D3: W. Geffeken, Glastech. Ber. 24, p. 143 (1951)

[0016] D4: H. Dislich, E. Hussmann, Thin Solid films 77 (1981), pp.129-139

[0017] D5: N. Arfsten, B. Kaufmann, H. Dislich, Patent DE 3300589 C2

[0018] D6: N. Arfsten, B. Lintner, et al., Patent DE 4326947 C1

[0019] D7: A. Pein, European Patent 0 438 646 B1

[0020] D8: I. Brock, G. Frank, B. Vitt, European Patent 0 300 579 A2

[0021] D9: Kienel/Frey (ed.), “Dünnschicht-Technologie [Thin layertechnology]”, VDI-Verlag, Düsseldorf (1987)

[0022] D10: R. A. Häfer, “Oberflächen- und Dünnschicht-Technologie[Surface and thin layer technology]”, Part I, “Coating of Surfaces”,Springer-Verlag (1987)

[0023] whose disclosure contents are fully incorporated in the presentapplication.

SUMMARY OF THE INVENTION

[0024] The object of the invention is to specify a coating for atransparent substrate, especially glasses, with which theabove-described disadvantages can be overcome.

[0025] In particular, one should achieve a UV filtering, on the onehand, without the use of UV or temperature-unstable polymer foils orvarnish, and, on the other hand, the antireflection of visible lightshould be much more broadband and color neutral at the same time.

[0026] As regards the UV filtering, one should achieve approximately thesame characteristics as for foil or varnish systems.

[0027] According to the invention, the object is solved by aninterference layer system that comprises at least four individuallayers, wherein the consecutive layers have different indices ofrefraction and the individual layers comprise UV and temperature-stableinorganic materials.

[0028] Especially preferred is an interference layer system of fivelayers with the structure: glass+M1/T1/M2/T2/S, wherein thehigh-refracting material T has an index of refraction in the range of1.9-2.3 at a wavelength of 550 nm, the low-refracting material S has anindex of refraction between 1.38 and 1.50, and theintermediate-refracting material M has an index of refraction in therange of 1.6-1.8, with layer thicknesses of the individual materials inthe ranges of 70 to 100 nm (M1), 30 to 70 nm (T1), 20 to 40 nm (M2), 30to 50 nm (T2), and 90 to 110 nm (S).

[0029] In one embodiment of the invention the highly refractive materialis titanium dioxide, the low-refracting material is silicon dioxide, andthe intermediate-refracting material is a mixture of these substances.

[0030] In an alternative embodiment, instead of titanium dioxide one canalso use niobium oxide Nb₂O₅, tantalum oxide Ta₂O₅, cerium oxide CeO₂,hafnium oxide HfO₂, as well as mixtures thereof with titanium dioxide orwith each other, as the high-refractive layers; instead of silicondioxide one can also use magnesium fluoride MgF₂ as the low-refractivelayer; and instead of Ti—Si oxide mixtures one can also use aluminumoxide Al₂O₃ or zirconium oxide ZrO₂ as the intermediate-refractivelayers.

[0031] As the transparent substrate, in a first embodiment, one can usesoft glass in the form of float glass, including a low-iron form.

[0032] As an alternative to this, one can also use hard glasses as thesubstrate, especially aluminosilicate and borosilicate hard glasses orquartz glass.

[0033] Besides the interference layer system, the invention alsoprovides a method for applying it onto a substrate.

[0034] In a first embodiment of the invention, the individual layers aredeposited by means of the dip method or the spin method of sol-geltechniques.

[0035] As an alternative to this, the layers can be deposited by cathodesputtering (for example), by physical vaporization, or by chemicalgas-phase deposition, especially plasma-supported.

[0036] Especially preferred, the interference coatings according to theinvention are deposited on transparent substrates comprising aninfrared-reflecting thermal protection coating, or transparent layerscomprising an interference layer system according to the invention areprovided with a thermal protection layer, so that a UV-reflectivethermal protection glass is obtained.

[0037] Thermal protection glasses are based on the principle ofreflection of the infrared heat radiation by a thin, electricallyconductive coating that is largely transparent in the visible range.Basically, tin oxide and silver-based layers are considered asheat-reflecting coatings.

[0038] Tin oxide can be deposited immediately after the float glassproduction—and application of a diffusion-inhibiting SiOx preliminarycoating—in the cool-down phase at around 600° C. by means of a sprayprocess. By doping with fluorine or antimony, surface resistances up to15 Ohms for a layer thickness of around 300 nm are achieved, so that amore than 80% degree of infrared reflection averaged out over thedistribution of 300 K thermal radiation is achieved.

[0039] As window glazing, therefore, this glass reflects back themajority of the thermal radiation into the space of a building.

[0040] The tin oxide deposited by spray pyrolysis during float glassproduction of interior double-pane glass, for example, must be protectedagainst cleaning, even though it has good mechanical and chemicalstability, since substances get worn down due to the relatively highroughness and hardness applied during cleaning processes, and drying ismade difficult.

[0041] In the double-pane insulated glass composite with an uncoatedflat glass pane, these glasses achieve a heat transfer value—dependingon the gas filling and the glass spacing—of up to k=1.6 W/m²K. Thedrawback is the only moderate visible transmission of 75% of such adouble-pane insulated glass for two panes with thickness of 4 mm, whichis predominantly attributable to the reflection at the boundary layers.The UV transmission, which should be as low as possible not only whenused as glazing for museums or textile shops, but also for residentialor office buildings, is 35% in the range of 280 to 380 nm.

[0042] Instead of doped tin oxide SnO₂:F,Sb, one can also use thetransparent semiconductor materials zinc oxide ZnO:Al (aluminum-doped)and indium oxide In₂O₃:Sn (tin-doped, “ITO”). Although ITO has aconsiderably lower electrochemical stability than tin oxide and requiresfurther treatments after the spraying process, zinc oxide cannot beproduced with sufficient electrical conductivity by means of a sprayprocess.

[0043] Silver-based heat-reflecting coatings achieve significantly morefavorable surface resistances down to less than 1 Ohm and, thus,infrared emission levels of 9 to 4%, at the limit down to 2%, so thatk-values of 1.1 to 1.4 W/m²K are possible on the basis of such a coatedpane in the double-pane insulated glass compound. The visibletransmission in this case is at most 76% and if the silver layers arethicker it drops to around 68% for k-values below 1.0 W/m²K. The UVtransmission is 36-19%.

[0044] The deposition of silver layers is more favorable in terms ofthermal reflection, but after the glass production it must be conductedby costly vacuum coating methods, and furthermore additional dielectriclayers surrounding the silver layer on both sides and possibly alsometal layers to improve the transmission and the long-term stability arerequired.

[0045] A further drawback is that the silver layer composite can only beused on the inside of double-pane insulated glasses, since there is nopermanent mechanical or even chemical stability with respect to cleaningprocesses.

[0046] The visible transmission of heat-reflecting insulated glasses, asdescribed above, is inadequate both in the case of tin oxide and forsilver-based layers. With an antireflection coating on all four boundarysurfaces of a double-pane insulated glass one can obtain glasses whosevisible transmission is boosted to 88%. However, the UV transmission isstill 25%.

[0047] By applying an interference layer system according to theinvention, one can obtain thermal protection glasses with lowtransmission in the UV range and high transmission in the visible range,so-called UV-reflective thermal protection glasses.

[0048] Preferably, a UV-reflective thermal protection glass according tothe invention comprises an infrared-reflecting thermal protection plateglass, coated with electrically conductive tin oxide, being provided onboth sides with a UV-reflective interference layer system, a single panethat is coated on one side with tin oxide and then provided on bothsides with the UV-reflective, broadband antireflecting multilayercoating [has] a (mean) visible transmission of 90% or more, as well as aUV transmission (280-380 nm) of 8% or less, while the thermal radiationproperties of the tin oxide remain unchanged.

[0049] As an alternative to this, UV-reflective thermal protectionglasses can be obtained with silver-based, heat-reflecting “low-e”layers, especially in the form of double-pane insulated glasses. If allthe other three glass surfaces except the low-e layer applied to theinside of a glass surface are provided with an interference layersystem, the visible transmission increases, for example, from 76% to85%—for unchanged heat-transfer value k—while the UV transmission isreduced from approximately 30% to around 4%.

[0050] If the low-e layer is applied on one side of a plate glasspreviously made antireflecting on both sides with an interference layersystem according to the invention, and combined with a second pane madeantireflecting on both sides with an interference layer system as adouble-pane insulating glass, the visible transmission is furtherincreased to 87%, while the UV transmission is reduced to 3%.

[0051] If the second pane is coated on one side with tin oxide prior tomaking both sides antireflecting with an interference layer system, thek-value will be reduced by around 0.2 W/m²K, i.e., from 1.0 to 0.8W/m²K, for example.

[0052] The visible transmission of a single pane coated with tin oxideon one side and made antireflecting with an interference layer system onboth sides, having a thickness of 4 mm, is 10% higher in absolute termsthan that of tin oxide thermal protection glass not made antireflecting,and 2 to 3% higher than that of uncoated float glass. At the same time,the UV transmission is lowered from approximately 45% to 8% withoutapplication of polymer varnish or foil.

[0053] If one combines a tin oxide-coated single pane provided with theUV-reflective interference layer system on both sides with an identicalsecond pane, the remaining UV transmission will be lowered to 3%, andonly a small residue of long-wave radiation will still be admitted inthe wavelength region of 360 to 380 nm.

[0054] At the same time, the thermal protection properties aresignificantly improved by the infrared reflection now at two tin oxidelayers, and k-values of around 1.2 W/m²K are possible, such as areotherwise achieved only with silver-based thermal protection glasses.The application of a double, IR-reflecting tin oxide layer is onlypossible because, thanks to the efficient broadband antireflection ofall four boundary surfaces with an interference layer system accordingto the invention, the total visible transmission is around 87% fornormal iron-containing float glass with two panes of 4 mm thicknesseach.

[0055] If—as has been customary thus far—only one layer of tin oxide isused in a double-pane thermal protection glass, the k-value remains atthe minimal 1.6 W/m²K, associated with a somewhat higher visibletransmission of 88% and a UV transmission of 4%.

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The invention shall now be described more closely by means of thefigures.

[0057] These show:

[0058]FIG. 1 the degree of reflection plotted against the wavelength asa function of the angle of incidence of the MIROGARD antireflection ofSCHOTT-DESAG, Grünenplan, according to the state of the art

[0059]FIG. 2 the degree of reflection plotted against the wavelength asa function of the angle of incidence of the AMIRAN antireflection ofSCHOTT-DESAG, Grünenplan, according to the state of the art

[0060]FIG. 3 the transmissibility of UV filters on soft glass accordingto the state of the art, as a function of wavelength

[0061]FIG. 4 the transmission spectrum of a system according to theinvention according to Example of embodiment 1

[0062]FIG. 5 the transmission spectrum of a system according to Exampleof embodiment 1 with several panes

[0063]FIG. 6 reflection characteristic of a system according to theinvention

[0064]FIG. 7 reflection characteristic of a system according to theinvention with an angle of incidence of φ=30°

[0065]FIGS. 8a, 8 b reflection characteristic of a system according tothe invention for an angle of incidence φ=8°

[0066]FIG. 9 reflection characteristic of a system according to theinvention according to Example 2

[0067]FIG. 10 reflection characteristic of a system according to theinvention according to Example 3

[0068]FIGS. 11a-11 c schematic representation of various thermalprotection glasses

[0069]FIGS. 12a-12 c transmission characteristic of thermal-protectionglasses according to Example 4

[0070]FIGS. 12d-12 e reflection characteristic of thermal protectionglasses according to Example 4

DESCRIPTION OF THE INVENTION

[0071]FIG. 1 shows the dependence of the degree of reflection R on theangle of incidence for the MIROGARD antireflection of Schott-DESAG. Themeasurements of the degree of reflection were plotted for various angles(12.5 to 50°) of the incident light vs. the normal line to the surface.

[0072]FIG. 2 shows the degree of reflection R for the three-layer AMIRANantireflections of Schott-DESAG AG, Grünenplan.

[0073] The systems according to FIGS. 1 and 2 show a strong dependenceof the degree of reflection on the angle of incidence of the light.

[0074]FIG. 3 shows the transmissibility of various UV filters accordingto the state of the art on soft glass as a function of wavelength.Normal window glass is practically nontransmissible below 290 nm,because of absorption, so that only an improved blocking in the UV-Bregion, i.e., to 315 nm, and primarily the blocking at 315 and 380 nmremains as a problem.

[0075] A MIROGARD three-layer antireflection without plastic foilalready provides a slight improvement in the UV blocking by absorptionand reflection as compared to uncoated glass. MIROGARD-Protect compoundglass is very effective as a UV-A blocker, as are TrueVue and Sky Glas,but TrueVue is very blue in reflection and significantly yellow intransmission.

[0076] Examples 1-3 of a system according to the invention withproperties that are improved compared to the prior art shall now bedescribed in detail:

EXAMPLE 1 Color-Neutral Filter

[0077] A UV filter with combined broadband antireflecting action isproduced on both sides of soft glass (d=3 mm, not iron-poor) by the dipmethod (sol-gel process), for the purpose of the most color-neutralappearance.

[0078] The coatings on both sides each consist of five individual layersand possess the structure: glass+M*+T+M+S. The individual layers areapplied identically on both sides in a dipping step.

[0079] The layers designated T contain titanium dioxide TiO₂, the coverlayer designated S contains silicon dioxide SiO₂, and the M layers areeach drawn from mixed S and T solutions.

[0080] The float glass substrate is carefully cleaned prior to thecoating. The dip solutions are each applied in climate-controlled roomsof 28° C. with humidity of 7 to 12 g/m³, the drawing speeds for theindividual layers M*/T/M/T/S being: 495/262/345/206/498 mm/min.

[0081] The drawing of each gel layer is followed by a baking in air. Thebaking temperatures and times are 180° C./20 min. after production ofthe first, second and third gel layers and 440° C./30 min. after thefourth and fifth layers.

[0082] In the case of the T layers, the dip solution (per liter) iscomposed of:

[0083] 68 ml of titanium-n-butylate, 918 ml of ethanol (abs.), 5 ml ofacetylacetone, and 9 ml of ethyl-butyrylacetate.

[0084] The dip solution for production of the S layer contains:

[0085] 125 ml of methyl silicate, 400 ml of ethanol (abs.), 75 ml ofH₂[O] (distilled), 7.5 ml of acetic acid, and is diluted with 393 ml ofethanol (abs.) after a resting time of around 12 h.

[0086] The coating solutions for production of the oxides withintermediate index of refraction are prepared by mixing the S and Tsolutions. The layer designated M in Example 1 is drawn from a dipsolution with a silicon dioxide content of 5.5 g/l and a titaniumdioxide content of 2.8 g/l; the corresponding oxide contents of the M*dip solution are 11.0 g/l and 8.5 g/l.

[0087] The wet chemistry sol-gel process used in Example 1, in the formof a dip process, enables the economical coating of large surfaces suchas architectural glass with interference filters, wherein thepossibility of coating both sides in a single work step and theproduction of mixed oxides with the particular desired index ofrefraction are of great advantage.

[0088] Panes can be coated either on both sides or, after covering oneside of the glass, just on one side.

[0089] Alternative coating methods are physical vaporization in highvacuum and modifications of this process in terms of ionic and plasmaassistance, and cathode sputtering.

[0090]FIG. 4 shows the transmission spectrum of a filter according tothe invention in the wavelength range of 280 to 480 nm, made accordingto Example of embodiment 1 (color-neutral filter). Even without the useof polymer substances, the dangerous UV-B region is completely blocked,and the UV-A region is more than ⅔ blocked, while only the lessdangerous range of 340-380 nm is around ⅓ transmitted. It should benoted that the harmfulness of UV radiation increases steadily towardshorter wavelengths.

[0091] The transmissibility in the wavelength range of 300 to 380 nm is15%, which is a UV attenuation by a factor of 4 as compared to anuncoated glass pane (around 60%). In the case of building glazings,however, double panes are usually employed, and less often triple panes.The use of multiple panes further improves the UV protectionconsiderably, as FIG. 5 shows.

[0092] In the case of double panes, each provided with the UV filteraccording to the invention on both sides, the transmissibility in therange of 300-380 nm is already reduced to 7%; for triple panes, a valueof 4% has been measured. At the same time, the reflection losses in theregion of visible sunlight for these architectural glazings are onlyaround 1% for single panes, and around 2% or 3% for double or triplepanes, respectively. As compared to uncoated glasses, this signifies a7% reduction of the reflection losses in absolute terms for the singlepane, and 14% and 21% for the double and triple panes, respectively.

[0093] Especially for glazings of museums and textile specialty shops,this creates a new state of the art, since the five-layer filter of theinvention represents only a relatively small additional expense comparedto the three-layer solution.

[0094] Furthermore, the filter according to the invention also solvesthe problem of realizing at the same time a color-neutralantireflection, which also guarantees a color-neutral antireflection atrather large viewing angles, thanks to the broad width of the range oflow reflection.

[0095]FIG. 6 shows the measured reflection characteristic of the filteraccording to the invention in the visible region of 380 to 780 nm as afunction of the viewing angle (12.5-50°). A comparison with FIGS. 1 and2 demonstrates the superiority of the solution according to theinvention as compared to MIROGARD and also AMIRAN in terms ofbroadbandedness, including in particular rather large viewing angles.This is also apparent from FIG. 7 by comparing the filter according tothe invention with these three-layer solutions for a given viewing angleof 30°.

[0096]FIGS. 8a and 8 b show the reflection spectrum for a viewing angleof 8° with different scales for R, and a wavelength range that isespecially enlarged in the UV direction: the average degree ofreflection in the region of 400 to 800 nm is 1%, the subjective colorimpression is essentially more neutral, especially for large viewingangles above 30°, than is the case with all traditional three-layerantireflections.

[0097] As FIG. 8a shows, the blocking action of the UV filter accordingto the invention is based primarily on reflection, and less onabsorption (UV reflector). The thus-produced optical filters not onlyexhibit the above-described wavelength-dependent transmission andreflection characteristic, but also are distinguished in particular by ahigh optical quality, they are free of cracks, opacities, and lightscattering, and provide a very color-neutral impression in reflection.Yet neither do they have any color-distorting effect in transmission,which is very important for picture glazings, for example.

[0098] The following service-life and application tests were carried outwith filters produced according to Example 1 with regard to anapplication in interior rooms:

[0099] Boil test (DIN 51 165), water of condensation/constant climate(DIN 50 017), salt spray/mist test (DIN 50 021), Cass test (copperchloride+acetic acid+NaCl)

[0100] and with regard to exterior application

[0101] Test for resistance to water of condensation, test for acidresistance, test for wear resistance (each time requirement category A).

[0102] The glasses coated according to the invention withstood the testsindicated here and can therefore be used both in interior spaces and inthe exterior field, for example, as architectural glazings.

[0103] The invention shall now be further explained by means of twoadditional examples of embodiment:

EXAMPLE 2 Green Antireflection

[0104] A UV filter with combined broadband antireflection action on softglass, for the purpose of a green residual reflection color, is producedanalogously to Example 1, but the first layer (M*) of Example 1 is nowreplaced by a layer M# which is drawn from a mixed silicon/titaniumsolution of modified composition. This solution has a silicon dioxidecontent of 11.0 g/l and a titanium dioxide content of 5.5 g/l. Due tothe relatively low titanium content, the M# layers thus produced have asomewhat lower index of refraction than M*.

[0105] As the drawing speeds for the individual layers M#/T/M/T/S thereare now selected: v=540/262/345/206/500 mm/min., obtaining an opticalfilter with a reflection characteristic according to FIG. 9, whichdiffers essentially from the filter of Example 1 only in the alteredresidual reflection in the visible range. The other properties of thefilter correspond to Example 1.

EXAMPLE 3 Blue-Violet Antireflection

[0106] A filter according to the invention, but with blue-violet colorof the residual reflection, is produced by the method and also with theindividual layers of Example 1, but with the following drawing speedsfor M*/T/M/T/S: v=525/247/302/194/470 mm/min. In this way, a filter witha reflection characteristic according to FIG. 10 is obtained. The otherproperties of the filter except for the altered color impression of theresidual reflection correspond to those of Examples of embodiment 1 and2.

[0107] The invention for the first time specifies a coating which makesthe glass/air interfaces antireflecting in the visible wavelength range(380-780 nm), preferably neutral in color, and at the same time itsubstantially improves the UV protection properties of transparentsubstrates in the wavelength range of UV-A (315-380 nm) and UV-B(280-315 nm).

[0108] Fields of application of the optical filters according to theinvention, besides the coating of glass panes, are the coating of lightbulbs in the light industry in order to improve the emitted visiblelight with color neutrality, especially including that at rather largeemission angles, while at the same time reducing the UV radiation. Thisapplies especially to gas discharge lamps with quartz glass bulbs, suchas metal halide bulbs, but also to a lesser extent to halogen lamps withquartz or hard glass bulbs.

[0109] Furthermore, tubular casings for lamps can be coated with thefilter according to the invention, and the filter can be used on planarfront panels of hard and soft glass.

[0110] An especially preferred usage of the interference layer systemsaccording to the invention is the coating of thermal protection glasses.

[0111]FIGS. 11a through 11 c represent application configurations ofUV-reflective thermal protection glasses according to the invention,wherein at least one side of a transparent substrate has been coatedwith a UV-reflective, interference system of five layers. Other layerstructures are also possible, as long as the individual layers containthe temperature-stable inorganic materials according to the invention.

[0112]FIG. 11a shows a simple system, a so-called single pane,comprising a substrate 100, on whose side facing the interior of a space102 has been deposited a thermal protection layer, in the present case,a tin oxide layer 104. On the outer side, the single pane comprises aninterference layer system 106 according to the invention. With such asystem, a transmission of more than 93% and a reflection of 2% in thevisible range are achieved, and in the UV range the transmission isreduced to less than 8% of the incident light.

[0113] The achievable k-value is 3.5 W/m²K.

[0114] By using two transparent substrates 100.1, 100.2, it is possibleto construct a double insulated glass pane, as shown in FIG. 11b. In thecase of the double insulated glass pane shown in FIG. 11b, only onetransparent substrate, the transparent substrate 100.1, is coated with aheat-reflecting tin oxide layer 104. The tin oxide layer 104 adjoins theinterior 108 of the double pane. On all four sides of the twotransparent substrates 100.1, 100.2, UV-reflective interference layersystems 106.1, 106.2, 106.3, 106.4 are deposited. With such a system, atransmission of more than 88% can be achieved with a reflection of lessthan 3% in the visible range. The transmission in the UV range is lessthan 4%, and the k-value is 1.6 W/m²K.

[0115]FIG. 11c, in turn, shows a system with two transparent substrates100.1, 100.2. The system is distinguished from the system of FIG. 11b inthat heat-reflecting layers 104.1, 104.2 are deposited on bothtransparent substrates 100.1, 100.2 on the inside 108 of the doubleinsulated glass pane. As with the embodiment according to FIG. 11b, allsides of the transparent substrates are coated with a 5-layerinterference system according to the invention.

[0116] In a system according to FIG. 11c, a transmission of more than87% and a reflection of less than 3% in the visible range are achieved.The transmission in the UV range is less than 3% and the k-value is 1.2W/m²K.

[0117] By UV region is meant primarily the wavelength region of 280 to380 nm. The transparent substrate used is a non-iron-poor float glasssubstrate of 4 mm thickness.

[0118] In the case of the interference layer systems which are depositedon the thermal protection glass for broadband antireflection, theuppermost of the five layers (S) next to the air has an index ofrefraction which is less than that of glass (n=1.52). The layer consistspreferably almost entirely of quartz glass (SiO₂, n=1.40-1.46). Thesecond and fourth layers (T)—viewing from S—consist of a material with ahigh index of refraction (n=2.0-2.3), preferably titanium dioxide(TiO₂). The M layers have an intermediate index of refraction ofn=1.6-1.8, which can be realized preferably by a mixed silicon/titaniumoxide.

[0119] The layer thickness of the M layer(s) next to the glass or tinoxide is 70-100 nm, depending on the configuration of the opticalfilter, that of the other M layers is 20 to 40 nm, the T layer closer tothe glass has a layer thickness of 30 to 70 nm, the T layer closer to Sis 30 to 50 nm, and the cover layer (S) is 90 to 110 nm.

[0120] These materials are deposited on the glass substrate preferablyby dip methods, for example, it is possible to coat a flat glass paneeither on both sides or, after covering one side of the glass, just onone side. The thermal protection glasses obtained with the interferencelayer system according to the invention shall now be explained moreclosely by means of examples of embodiment:

EXAMPLE 4

[0121] A plate glass coated on one side with tin oxide (d=3 mm, notiron-poor, surface resistance 15 Ohms) is provided on both sidesidentically with a UV-reflective 5-layer broadband antireflectioncoating by means of the dip method (sol-gel process) in keeping withExample 1 mentioned above, so that a structure STMTM/glass/tinoxide/MTMTS is formed.

[0122] The plate glass thus improved has a wavelength-dependenttransmission according to FIGS. 12a-12 c and a reflection characteristic(when the tin oxide side is illuminated) according to FIGS. 12d and 12e. The coatings have a high optical quality and are free of cracks,visible opacities, and light scattering.

[0123] One particular feature of the invention is the smoothing out ofthe tin oxide surface, which is relatively rough prior to the coating,thanks to the 5-layer antireflection coating: while the uncoated tinoxide surface is characterized by roughness values ofR_(a)/R_(z)/R_(max)=0.02/0.30/0.52 μm, these values are reduced to0.02/0.08/0.10, by the antireflection coating, which corresponds to thevalues for uncoated float glass.

[0124] As cleaning tests show, this also makes possible an applicationof the tin oxide layer to the outside of glazings, and thus in thesimplest instance a single-pane thermal protection glazing, as shown inFIG. 11a. This is of special interest for exhibition halls, for whichthus far it was only possible to use single-pane glazings without aheat-reflecting layer. But since the heat-reflection function isimpaired by a coating of water, the tin oxide side must be directedtoward the interior of the building.

[0125]FIG. 12c shows that, in the visible range, only a moderateantireflection action of around 1% is achieved with the coated glass 100according to the invention—as compared to fully uncoated float glass102—but the heat transfer coefficient is lowered from 5.8 W/m²K toaround 3.5 W/m²K, and thus approaches the k-value of an uncoatedinsulated glass double pane of around 3.0 W/m²K. The UV transmission(FIG. 12b) is lowered from 55% for uncoated float glass 102 or 40% forfloat glass with AMIRAN antireflection on both sides, to 8% (not shownin FIG. 12b).

[0126] As FIG. 12a shows, above a wavelength of around 2500 nm in theinfrared the optical properties of the tin oxide layer are not alteredby the UV-reflective antireflection layers. In the intermediate range ofthe near infrared (NIR, 780-2500 nm), a considerable sun protectionaction is achieved as compared to uncoated K-glass 104, since thelowering of the transmission in the range of 1050 to 2400 nmsignificantly outweighs the transmission gain in the range of 780-100nm, both times weighted with the incoming radiation spectrum of the sun.

[0127] The single pane coated with an interference layer systemaccording to the invention according to Example 4 can also be used toconstruct double-panel insulated glass.

[0128] The single pane according to Example 4, furthermore, can be usedas an electric heating panel, if the tin oxide layer is grounded as anantielectrostatic element, or for reflection of electromagnetic waves.

[0129] The following service-life and application tests according to DINEN 1096-2 have been carried out on the filter prepared according toExample 1: testing for resistance to water of condensation, testing foracid resistance, testing for salt spray/mist (neutral), testing for wearresistance, each time requirement category A, and the requirement forarchitectural glazings has been fulfilled.

[0130]FIGS. 12d-e show the reflection curves for thermal protectionglass 104 as compared to thermal protection glass 104 coated with theinterference layer system according to the invention.

[0131] Additional examples of embodiment for UV-reflective thermalprotection glass shall be specified below.

EXAMPLE 5

[0132] A plate glass coated on one side with tin oxide according toExample 4 is provided with a modified 5-layer antireflection, therebyforming the structure STMTM/glass/tin oxide/TMTS, which is equivalent toomitting the thick M layer on the tin oxide side. This is achieved byfirst gluing together two plate glasses at the edges by the tin oxidesides, then coating the combination with an M layer according to Example4 by the dip method, separating the panes, and then further coating eachof them on both sides with the structure TMTS, all of this according toExample 4.

[0133] The UV-reflective thermal protection glass according to Example 5according to the invention has largely the same properties as thatproduced by Example 4; the major difference is an improved transmissionin the visible range of 92%, which is accomplished by a mean visiblereflection improved to 1.9%.

EXAMPLE 6

[0134] The method is the same as in Example 5, except that the drawingspeed to produce the T-layer closer to the glass is reduced from 262mm/min. to 220 mm/min., and thus the thickness of this layer is reducedby around 11%. In this way, the mean visible residual reflection isfurther reduced to 1.5%, so that the visible transmission is furtherimproved to 93%, while the other properties are unchanged in comparisonto Examples 4 and 5.

[0135] As is apparent, for example from FIGS. 6, 7, 8 b, 9 and 10 aswell as FIGS. 12b-e, the reflectivity of the interference layer systemin the wavelength range of 300-380 nm is ≧20% and the reflectivity inthe wavelength range of 450-800 nm is ≦5%.

What is claimed is:
 1. A UV-reflective interference layer system fortransparent substrates with broadband antireflection in the visiblewavelength range, the interference layer system comprising at least fourindividual layers, wherein consecutive layers have different indices ofrefraction and the individual layers contain UV and temperature-stableinorganic materials, characterized in that the interference layer systemcomprises five individual layers with the following structure:substrate/M1/T1/M2/T2/S, wherein substrate designates the transparentsubstrate, M1, M2 denote layers with intermediate index of refraction,T1, T2 denote layers with high index of refraction, S denotes a layerwith low index of refraction, and for a reference wavelength of 550 nmthe indices of refraction of the individual layers lie in the followingrange: n_(low)≦1.6 1.6>n_(intermediate)<1.8 1.9≦n_(high) and thethickness of the individual layers lies in the following range: for thelayer M1: 70 nm≦d_(M1)≦100 nm for the layer T1: 30 nm≦d_(T1)≦70 nm forthe layer M2: 20 nm≦d_(M2)≦40 nm for the layer T2: 30 nm≦d_(T2)≦50 nmfor the layer S: 90 nm≦d_(S)≦110 nm.
 2. The interference layer systemaccording to claim 1, further characterized in that the inorganicmaterials are inorganic oxides.
 3. The interference layer systemaccording to claim 1, further characterized in that the inorganic oxidesare largely transparent above a wavelength of light of 320 nm.
 4. Theinterference layer system according to claim 1, further characterized inthat the individual layers comprise one or more materials or mixtures ofthe following groups of inorganic oxides: TiO₂, Nb₂O₅, Ta₂O₅, CeO₂,HfO₂, SiO₂, MgF₂, Al₂O₃, ZrO₂.
 5. The interference layer systemaccording to claim 1, further characterized in that the layers comprisethe following materials: the high-refracting layer with n_(high), TiO₂the low-refracting layer with n_(low), SiO₂ and theintermediate-refracting layer with n_(intermediate), a mixture of TiO₂and SiO₂.
 6. The interference layer system according to claim 1, furthercharacterized in that the high-refracting individual layers withn_(high) comprise one or more of the following materials: Nb₂O₅, Ta₂O₅,CeO₂, HfO₂, as well as mixtures of these with TiO₂, the low-refractinglayers contain the following materials: MgF₂ or mixtures of MgF₂ withSiO₂, and the intermediate-refracting layers contain one or more of thefollowing materials: Al₂O₃, ZrO₂.
 7. A UV-reflective glass with aninterference layer system according to claim 1 and a transparentsubstrate, wherein the transparent substrate is soft glass in the formof float glass, including iron-poor form.
 8. A UV-reflective glass withan interference layer system according to claim 1 and a transparentsubstrate, wherein the transparent substrate is a hard glass, especiallyaluminosilicate and borosilicate hard glass.
 9. A UV-reflective glasswith an interference layer system according to claim 1 and a transparentsubstrate, wherein the transparent substrate is quartz glass.
 10. AUV-reflective thermal protection glass, comprising at least onetransparent substrate, wherein the substrate has a heat-reflectingcoating on at least one side, which has a surface resistance <20 Ω,characterized in that the substrate, which has a heat-reflecting coatingon at least one side, moreover has at least one UV-reflectiveinterference layer system according to claim
 1. 11. The UV-reflectivethermal protection glass according to claim 10, further characterized inthat the UV-reflective interference layer system is deposited onto theheat reflecting interference layer system.
 12. The UV-reflective thermalprotection glass according to claim 10, further characterized in thatthe UV-reflective interference layer system is deposited directly on thesubstrate, and a heat-reflecting layer with a surface resistance <20 Ωis deposited on the UV-reflective interference layer.
 13. TheUV-reflective thermal protection glass according to claim 10, furthercharacterized in that the UV transmission of the thermal protectionglass in the UV range of 280-380 nm is less than 8% and in the visiblewavelength range it is greater than 90%.
 14. The UV-reflective thermalprotection glass according to claim 10, further characterized in thatthe heat-reflecting coating comprises one or more of the followingmaterials: SnO₂:F,Sb ZnO:Al In₂O₃:Sn Ag-based coating.
 15. TheUV-reflective thermal protection glass according to claim 10, furthercharacterized in that the heat transfer value of the thermal protectionglass is smaller than 3.5 W/m²K.
 16. The UV-reflective thermalprotection glass according to claim 10, further characterized in thatthe UV thermal protection glass comprises two transparent substratesyielding a double-pane insulated glass, wherein at least one side of oneof the transparent substrates has a heat-reflecting layer and at leastthree sides of the two substrates comprise the reflective interferencelayer system.
 17. The UV-reflective thermal protection glass accordingto claim 16, further characterized in that the double-pane insulatedglass has a small k-value of less than 1.0 W/m²K and a UV transmissionof less than 4% and a visible transmission in the visible wavelengthrange of greater than 85%.
 18. A method for coating a substrate, atransparent substrate with a coating system according to claim 1,characterized in that the deposition of the individual layers isperformed by a dip or spin method of sol-gel techniques.
 19. A methodfor the coating of a substrate, a transparent substrate with aninterference layer system according to claim 1, characterized in thatthe deposition of the individual layers is performed by means of cathodesputtering, physical vaporization, or chemical gas-phase deposition,especially ion or plasma-assisted.
 20. The method according to claim 18,further characterized in that the substrate is coated on both sides. 21.The method according to claim 18, further characterized in that one sideof the substrate is covered and the substrate is only coated on oneside.
 22. Use of an interference layer system according to claim 1 forthe coating of panes for glazings.
 23. Use of an interference layersystem according to claim 1 for the coating of light bulbs in thelighting industry.
 24. Use of an interference layer system according toclaim 1 for the coating of tubular casings for lamps or front panelsmade of hard or soft glass.